GDF15 and glaucoma: Growth differentiation factor 15 (GDF15), a member of the TGF-β superfamily, was found to be increased in the aqueous humor of POAG patients, and also significantly associated with worse functional outcomes in individuals with POAG and PEXG, being therefore proposed as marker of glaucoma severity that may be generalizable to multiple types of glaucoma, regardless of the underlying etiology [53,54].